1. Field of the Invention
The present invention relates to a rotary current-collecting device having a combination of a collector and brushes, and more especially to a rotary current-collecting device characterized by the material of the collector. The present invention also relates to a rotating anode X-ray tube having such a rotary current-collecting device.
2. Description of the Related Art
The rotary current-collecting device is known as typically a combination of a commutator and brushes as in a electric motor or a combination of a slip ring and brushes for power supply to a rotary shaft. The commutator and the slip ring are rotary members which are called as a collector. On the other hand, the brushes are stationary members which come into sliding contact with an outer peripheral surface of the collector. An electric current flows between the collector and the brushes during the sliding contact.
The collector and the brushes are made of an electrically conductive material. The collector is often made of metal while the brush is often made of graphite for a relatively high-current purpose. The lifetime of the rotary current-collecting device depends upon the amount of abrasion of the collector and the brushes, and therefore it is important for a long lifetime to select a suitable material which has a low electrical resistance during the sliding contact and shows a small amount of abrasion. A number of techniques have been developed for reducing abrasion of the rotary current-collecting device. Among those techniques, one prior art focusing attention on glassy carbon is known and disclosed in Japanese patent publication No. 6-153459 A (1994), in which the brush is made of a metal-graphite compound including graphite and copper in major components and such a brush is manufactured in a manner that graphite powder and copper powder are mixed with glassy carbon powder of less than 10 percent by weight and are then sintered. The thus manufactured brush achieves reduced abrasion of the brush and the commutator.
In the prior art described above, the addition of a small amount of the glassy carbon to the metal-graphite brush can reduce abrasion of the brush and the commutator. The reduction of abrasion is, however, inadequate. Especially, an amount of brush abrasion is large as a nearly tenfold amount of commutator abrasion.